Growing characters and tribological properties of microarc oxidation composite coating containing Cr₂O₃ microparticles on Ti6Al4V alloy

The microarc oxidation (MAO) composite coating containing Cr₂O₃ microparticles on Ti6Al4V alloy was prepared by co-deposition in the electrolyte with Cr₂O₃ microparticles addition. The growing characters of the composite coating and deposition styles of Cr₂O₃ microparticles were studied by SEM, XRD and EDS. The tribological behaviors of the composite coating formed at different oxidation time were evaluated using abrasive tests. The results show that the thickness of the composite coating is linearly increased in 30 min; afterwards the growth rate of the composite coating decreases evidently, and large lumps of Cr₂O₃ agglomerate appear on the film surface in the later stage. The composite coating is mainly composed of rutile-TiO₂, anatase-TiO₂ and Cr₂O₃ phase. The anatase-TiO₂ decreases gradually, the content of rutile-TiO₂ increases firstly and then becomes stable, but the diffraction peak of Cr₂O₃ phase strengthens continuously with the increasing of oxidation time. Besides, the wear-resistance of the composite coating is improved firstly and then reduced with the increasing of oxidation time. The composite coating formed at 20 min exhibits good antifriction property, whose friction coefficient is 0.05~0.2. In the process of MAO, Cr₂O₃ microparticles may be adsorbed directly on the surface of the molten oxidation coating, or may be caught and locked into the irregular pores of oxidation coating. In additon, some Cr₂O₃ particles may be wrapped by molten products generated in the microarc discharge channel, and solidified together into the oxidation coating.